1. Field of the Invention
The present invention relates generally to metering gear pumps, and more particularly to spur gear mechanisms, which are used within gear pumps for pumping and measuring tasks. A method for reducing pulsations in pumping tasks is also included.
2. Description of Related Art
Gear pumps belong to a class of devices known as continuous displacement devices which are used to increase and decrease pressure in a system. Metering (or dosimetric) pumps are a subtype of gear pumps and are used to quantitatively measure certain aspects of the system. Gear pumps and metering pumps have long been in use and are commonplace throughout a variety of industries today.
As used throughout this specification and appended claims, the following gear-related terms have the meanings indicated:
"Addendum" means the radial distance from the pitch circle to the outside circle of the gear.
"Addendum radius" means the maximum radius of the gear (pitch radius plus addendum).
"Dedendum" means the radial distance from pitch circle to bottom of space between teeth.
"Dedendum radius" means the radius of circle defining bottom of space between teeth (pitch radius minus dedendum).
"Tooth width" means the arc of pitch circle subtending width of a tooth.
"Space width" means the arc of pitch circle subtending space between teeth.
"Circular pitch" means the segment of arc of pitch circle assigned to one tooth and one space.
"Diametral pitch" means the number of teeth on a gear divided by its pitch diameter.
"Face of gear" means the thickness of the gear measured parallel to the axis of rotation.
"Face of tooth" means the contacting surface of tooth from pitch circle to addendum circle.
"Flank of tooth" means the contacting surface of tooth from pitch circle to dedendum circle.
"Fillet" means the rounded corner between flank and dedendum circle.
A wide variety of gear types exist. Spur gears, for example, have teeth on their outer circumference which are parallel to the axis of rotation. Annular gears teeth positioned around the interior surface of ring. Bevel, helical (including herringbone), spiral, and worm gears are additional types of gearing mechanisms. Disadvantages exist with respect to each of the specified gearing mechanisms. Helical gear systems generate an undesirable axial thrust component which causes both a given side plate and a gear to become worn, resulting in an undesirable increased side clearance between the side plate and the gear. In addition, precision grinding is expensive. Although herringbone gear systems generate no axial thrust, they are also expensive to precision grind. Herringbone gear teeth are also subject to distortion at high temperatures which can result in ineffective sealing between teeth. Single spur gear systems do not generate axial thrust but do create unwanted pulsations during the engagement of each successive tooth and fillet.
Gear pumps function by moving matter, typically liquid, in each fillet around the periphery of the gear and expelling it by engagement of the tooth of the adjacent gear into the fillet at the point of engagement. A continuous seal is formed between the mating teeth. Minimal side and tip clearances prevent the travel of significant quantities of liquid from the high pressure side to the low pressure side of the pump. Gear pumps may employ different types of gears and may be configured in a variety of ways (e.g., multiple-gear, planetary, staged or tandem).
Measuring pumps are utilized in continuous extrusion process systems such as fiber, film, form and wire extrusion, perfume, and additive chemical production. Form and wire extrusion is a type of profile extrusion whereby the output of the measuring pump is formed by creating a pre-determined shape surrounding a wire(s) and/or a continuous extruded form. These applications require that pulsations be kept to a minimum. In addition, since high amplitude pulsations emit detectable amounts of acoustical energy, minimal pulse pumps are required in specialized hydraulic systems used in marine applications.
Applicant is aware of the following U.S. Patents concerning gear pumps generally.
______________________________________ U.S. Pat. ISSUE No. INVENTOR DATE TITLE ______________________________________ 3,272,140 Curry et al. 09/13/1966 METERING PUMP 4,761,125 Inagaki et al. 08/02/1988 TWIN-SHAFT MULTILOBED TYPE HYDRAULIC DEVICE 4,907,954 Slupski 03/13/1990 MULTIPLE LOBED PISTON PUMP WITH ANGULARLY AND AXIALLY DIS- PLACED SEGMENTS AND THROTTLE VALVE 621,280 Pitt 03/14/1899 ROTARY PUMP ______________________________________
Curry relates to a positive displacement metering pump with a metered output stream which is purported to be substantially free of pulsations. The pumping apparatus comprises a gear pump housing having an inlet port, first and second pairs of meshed gears within the housing, and means for defining a common discharge port for the output streams of the first and second pairs of gears. The second pair of gears is aligned with respect to the first pair of gears so that the teeth of the second pair of gears are angularly displaced one-fourth pitch with respect to the corresponding teeth on said first pair of gears.
Curry's first embodiment includes a separator plate between pairs of gears. He states that in a second embodiment the plate could be eliminated "if each tooth tip extends over an arc of at least one-fourth of the pitch angle, so that each tooth overlaps the corresponding tooth on the adjacent gear on the same shaft over their entire depths, when viewed parallel to the axis about which the gears revolve." Although Curry's disclosure is somewhat ambiguous, it appears that he proposed either or both of the following: (1) the teeth on adjacent gears be displaced one-fourth of the pitch angle (i.e., the angle defined by lines connecting corresponding points on adjacent teeth with the gear center) with respect to each other; and (2) the tips of the teeth extend over an arc on the gear circumference of at least one-fourth of the pitch angle. Proposition (1) is equivalent to suggesting that the teeth on adjacent gears be displaced as shown in FIG. 8 herein, that is, aligning one, and only one, intersecting edge of a tooth tip and face of a tooth with one intersecting edge of a tooth tip and face of a tooth of an adjacent gear. Experimentation reveals that this configuration does not form an adequate seal to function as a gear pump and is consequently non-functional for reducing pulsations in dosimetric pumps. Proposition (2) amounts to imposing a constraint on the size of the teeth of a gear relative to pitch angle. The present invention imposes no such restraint.
Inagaki et al. teaches a twin-shaft multi-lobed type hydraulic device, such as a device used as a compressor for a vehicle air-conditioner or as an air pump.
Slupski relates generally to rotary positive displacement pumps. The object is to reduce the vibration and noise output of such pumps. Slupski includes cooperating pistons having segments which are angularly displaced from each other. Slupski appears to be limited to pumps which include a separator plate between the gear pairs.
Pitt relates to pumps, and more particularly to that type of pump which embodies intermeshing gears or pistons arranged in pairs and suitably encased, the casing having an induction-port in its bottom and an eduction-port in its top. This patent is mentioned for the purpose of full disclosure, but clearly it is not directly relevant to the present invention.
None of the aforementioned related art patents appear to disclose the structure, operation, and result of the present invented split gear pump. In particular, none of the patents disclose at least two pairs of meshed gears, each pair of gears (first pair) being so aligned with respect to at least one adjacent pair of gears (second pair) that the teeth of the second pair are angularly displaced less than one-fourth pitch with respect to the corresponding teeth on the first pair.